Method and device for removing a component from solid particle material by extraction

ABSTRACT

In order to remove a component from solid particle material by extraction, use is made of a column with one or more tubes which extend between the ends of the column, at least one filter being fitted in the wall of each tube. The particle material is fed in at a first end of the column and, forced by hydraulic pressure, moves along the abovementioned tubes to scraping means fitted at the second end of the column. Extraction liquid is fed into the column at the abovementioned second end and flows in countercurrent to the particle material in the direction of the abovementioned first end of the column. Extraction liquid with component from the particle material dissolved in said extraction liquid passes by way of the above mentioned filters into the abovementioned tubes and flows in countercurrent to the particle material to an outlet at the abovementioned first end. The particle material is scraped off at the abovementioned second end by the scraping means.

REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/NL99/00651 filed Oct. 20, 1999.

The invention relates in the first instance to a method for removing acomponent from a solid particle material by extraction, in which anextraction liquid is brought in flowing contact with the particlematerial inside a column in which at least one tube extends, and theparticle material is fed in at the first end of the column and—forced byhydraulic pressure—moves as a packed porous bed to scraping means fittedat the second end of the column, and the extraction liquid is fed intothe column at the above-mentioned second end and flows in countercurrentto the particle material in the direction of the above-mentioned firstend of the column, and the particle material is scraped off at theabove-mentioned second end by the above-mentioned scraping means.

Such a method is disclosed in FR-A-2.213.080.

In the case of a known method the particle material for extraction andthe extraction agent are in a number of successive vessels, the vesselswith particle material being conveyed batchwise in a certain directionand the extraction agent being pumped in the opposite direction from onevessel to the next. The particle material gradually loses theabove-mentioned component, and the extraction agent takes up saidcomponent. The bed of particle material stops in each vessel and theliquid extraction agent flows through it. Although on a macro scale thiscan be described as a countercurrent process, on a micro scale there isno question of countercurrent here. The process is relatively slow, andthe extraction yield leaves something to be desired.

Another known process is described by George C. Blytas in “ChemicalEngineering Communication”, 1990, Vol. 88, pp. 127-151, under the title“Continuous countercurrent solid-liquid contacting in rotary disccontactors”. A column with discs placed above one another is describedin this article. The force of gravity causes solid particles of resin tofall from the top to the bottom of the column and to absorb benzene froman upward-flowing supply stream. Situated between the perforated platesare siring elements which rotate at high speed in order to suspend theparticle material. The particle material consists of, for example,resin. This process is also slow and can be carried out only when theparticle material settles sufficiently in the extraction agent.

The object of the invention is to provide a method of the type describedin the preamble which leads to a relative high speed and a relative highyield and which does not have the disadvantages of the known methods.

According to the invention, the method is characterized in that at leastone filter is fitted in the wall of each tube and that extraction liquidwith component from the particle material dissolved in said extractionliquid passes by way of the above-mentioned filter or filters into theabove-mentioned tube and flows in countercurrent to the particlematerial to an outlet at the above-mentioned first end, said outletbeing connected to the tube, and that the scraped particles aredischarged via a washing chamber.

It is important that the solid bed of particle material is moved, forcedby hydraulic pressure, in the column, which hydraulic pressure isproduced as a result of the filtration resistance of the porous bed ofparticle material present in the column. The process is preferably acontinuous countercurrent process. The main advantage is that arelatively high speed and a high yield are achieved. The material to beextracted is, for example, crushed rapeseed, and the extraction agenthexane. The hexane extracts the oil from the rapeseed.

In order to ensure that a certain extraction by immersion is achievedbefore the particle material is conveyed into the column, the particlematerial is mixed beforehand in a tank with extraction agent or amixture of extraction agent and the above-mentioned component.

The particles which are scraped off at the above-mentioned second end ofthe column and pass into a washing chamber situated below the scrapingmeans are taken up in a circulating stream of clean extraction agent.

Part of the extraction agent, and a component dissolved therein leavingthe tubes at the above-mentioned first end of the column, can beconveyed to the particle material to be fed into the column, while mostof said extraction agent is conveyed to a separator for separatingextraction agent and component from each other.

In order to limit the consumption of extraction agent, the mixture ofextraction liquid and extracted particle material (extracted meal)leaving the column at the above-mentioned second end is separated, andthe extraction agent resulting therefrom is pumped back to theabove-mentioned second end.

A better yield is generally achieved when the extraction agent is at araised temperature.

The invention also relates to a device for removing a component fromsolid particle material by extraction according to claim 1, comprising acolumn in which at least one tube extends, said column having a firstand second end, means for feeding extraction liquid into the column atthe second end thereof, and scraping means at the first end of thecolumn for scraping off particle material from a packed porous bed.

Such a device is also disclosed in FR-A-2.213.080.

According to the invention the device is characterized in that in thewall of each tube at least one filter is fitted, that at the first endthe outlet is connected to the tube or tubes, and a washing chamber issituated near the scraping means so that scraped off particles aredischarged via said washing chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show two embodiments for removing a component from a solidparticle material by extraction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be explained in greater detail with reference totwo figures, in which diagrammatic embodiments of the device are shown.

In the figures the reference numerals denote the following:

FIG. 1

1=column

2=tube fitted in the column 1

3=filter fitted in the wall of the tube 2

4=mixing tank

5=line between mixing tank 4 and column 1

6=pump fitted in the line 5

7=separator for separating extraction agent and component (product)

8=line between the tube 2 and the separator 7

9=line branched off from the line 8 and running to the mixing tank 4

10=supply line to the mixing tank 4

11=rotary scraping knife

12=washing chamber

13=separator for separating particle material and extraction liquid

14=line going out from washing zone

15=pump in line 14

16=stock tank for ordinary extraction agent

17=hexane line from the separator 13

18=line for supplying hexane to washing zone 12

19=pump in line 18

20=supply line for extraction liquid to tank

21=outlet for extracted particle material coming from the separator 13

22=recirculation line

23=pump in line 22

FIG. 2

24=closed settler

25=discharge line of settler 24

27=hexane line from separator 13

28=pump in line 25

29=open hexane tank

30=hexane supply and discharge line between open hexane tank 29 andcircuit line 18

31=pump in line 30

The solid-liquid extraction process according to the invention will beexplained in greater detail with reference to the extraction of oil fromrapeseed by means of the extraction liquid n-hexane, although theprinciple of the invention offers many kinds of potential applications,such as the extraction by acid of metals from ore, the extraction ofimpurities from solids, and the extraction of pharmaceutically orchemically valuable constituents from solids.

In the case of the embodiment according to FIG. 1 crushed rapeseed isfed into the mixing tank 4 by way of the line 10, and hexane with oildissolved therein is fed into the mixing tank 4 by way of the line 9.The pumpable mixture of these constituents is conveyed by means of pump6 and the line 5 into the column 1, with the result that a packed porousbed is produced in the column. The pure solvent (extraction agent)hexane is fed into the bottom of the column by means of the pump 19 byway of the line 18. Part of this pure hexane runs upwards in the column.As a result of the liquid flow through the packed bed and the filtrationresistance of the bed, a hydraulic pressure occurs above the bed, whichhydraulic pressure supplies the conveyance force for moving the beddownwards in countercurrent and into contact with the upward-flowinghexane in the bottom zone of the column (between the scraping knife 11and the filter 3).

The rotary scraping knife 11 scrapes off the seed bed layer by layer inthe bottom of the column.

During the countercurrent between seed bed and hexane, oil from the seeddissolves in the hexane. This hexane oil solution is conveyed by way ofthe filter 3 into the tube 2 and from there by way of the line 8 to aseparator 7, in which hexane and oil are separated from each other. Theoil is discharged as a product, and the hexane—possibly after undergoingan after-purification—can be conveyed to the tank 16. Some of thehexane-oil mixture can be conveyed by way of the branch line 9 to themixing tank 4. Some of the filtrate (hexane solution) can berecirculated, if desired, by means of pump 23 and line 22.

The particles scraped off by the scraping knife 11 pass into the cleanhexane liquid in the washing chamber 12 below the knife.

The delivery of clean hexane flowing in countercurrent to the bed can beset by means of pumps 19 and 15. This hexane delivery is called theextraction delivery. As an example, the volume proportions can be asfollows: pump 15 discharges per unit time 5 litres of clean hexane andscraped-off seed—which through extraction has released a large part ofthe oil and is called extracted meal—from the washing chamber 12. Theseare separated in separator 13 into one litre of extracted meal to bedischarged, said extracted meal being discharged by way of line 21, and4 litres of clean hexane, which is conveyed to the tank 16. From saidtank 16 five litres of clean hexane is conveyed by means of pump 19 andby way of line 18 to the washing chamber 12, of said five litres onelitre of hexane being conveyed upwards in countercurrent to the bed. Theprocess described is continuous. By pumping more or less clean hexaneinto the washing chamber by means of pump 19, the extraction deliverycan be increased and reduced respectively, the minimum quantity beingslightly higher than the quantity of hexane required for the dischargeof the extracted meal (in this example four litres). This makes theextraction of oil from the seeds quicker and cheaper than is the case inknown processes. For the invention it is important that a component isremoved by a liquid from solids by extraction in countercurrent on amicro scale and that the liquid with the component dissolved therein isdischarged by way of a filter and a tube. Instead of one tube 2, severaltubes 2, preferably uniformly distributed over the cross section of thecolumn 1, can also be used. Increasing the diameter of the column at thesame time will increase the capacity for the processed particle material(capacity is directly proportional to the diameter squared). It will beclear that a certain extraction occurs beforehand by immersion duringthe mixing of the particle material and the extraction agent in themixing tank 4.

The miscella conveyed to the separator 7 by way of the tube 2 and theline 8 comprises, for example, 70% hexane and 30% oil.

The results of the process are dependent, inter alia, upon thetemperature of the hexane and the residence time in the column, theparticle size of the crushed seed, the level of the extraction deliveryand the vertical distance between scraping knife and filter. Increasingthe temperature of the hexane (for example, to 50° C.) leads to asignificant reduction of the residual oil content in the seed, forexample from 6.1 to 3.8%, assuming an oil content of 47.2% in thecrushed seed which through the immersion extraction in mixing tank 4 hasdecreased to a value between 29.6 and 32.8% at the time of infeed at thetop of column 1.

The circuit 12, 14, 24, 18, 19 below column 1 is filled completely withclean hexane at the time of start-up. As a result of the bed beingscraped off in the column, the scraped-off seed (extracted meal) goesinto this circuit, with the result that the extracted meal pushes anequal volume of clean hexane out of the circuit. This clean hexane isforced to flow upwards in the column in countercurrent to the bed. Theclosed settler in the embodiment according to FIG. 2 is operated in sucha way that the discharge of the settled extracted meal by way of line 25and pump 28 ensures that the settled extracted meal remains at aconstant height in the settler 24. Moreover, the settler 24 is operatedin such a way that completely or almost completely particle-freeextraction agent is extracted at the top by way of line 18. Theextracted meal discharged from the settler is separated from the hexanein separator 13. After the separation, the hexane is recirculated to thecircuit by way of the line 27, tank 29, line 30 and pump 31. Thesuppletion of hexane to the circuit is at least equal to the dischargeof extracted meal plus hexane from the bottom of settler 24, so that thecircuit always remains filled. For the rest, the suppletion delivery ofclean hexane by way of line 30 and pump 31 is freely adjustable. As aresult, the extraction delivery, i.e. the flow of clean hexane leavingthe circuit by way of the column in countercurrent to the downwardsmoving bed, is also freely adjustable. It is therefore not necessarilythe case that the extraction delivery of clean hexane is equal in volumeflow to the volume flow of scraped-off seed. The complete arrangementaccording to the embodiment in FIG. 2 is operated continuously.

What is claimed is:
 1. Method for removing a component from a solidparticle material by extraction, in which an extraction liquid isbrought in flowing contact with the particle material inside a column inwhich at least one tube extends, and the particle material is fed in atthe first end of the column and—forced by hydraulic pressure—moves as apacked porous bed to scraping means fitted at the second end of thecolumn, and the extraction liquid is fed into the column at theabove-mentioned second end and flows in countercurrent to the particlematerial in the direction of the above-mentioned first end of thecolumn, and the particle material is scraped off at the above-mentionedsecond end by the above-mentioned scraping means, characterized in thatat least one filter is fitted in the wall of each tube and thatextraction liquid with component from the particle material dissolved insaid extraction liquid passes by way of the above-mentioned filter orfilters into the above-mentioned tube and flows in countercurrent to theparticle material to an outlet at the above-mentioned first end, saidoutlet being connected to the tube, and that the scraped particles aredischarged via a washing chamber.
 2. Method according to claim 1,characterized in that the particle material fed in at theabove-mentioned first end of the column is mixed beforehand in a tankwith extraction liquid or a mixture of extraction liquid and theabove-mentioned component, with the result that immersion extractionoccurs.
 3. Method according to claim 1, characterized in that a streamof clean extraction liquid is circulating inside said washing chambersituated below the scraping means.
 4. Method according to claim 1,characterized in that the extraction liquid, and the component dissolvedtherein leaving the tubes at the above-mentioned first end of thecolumn, are conveyed to a separator in order to separate extractionliquid and component from each other.
 5. Method according to claim 4,characterized in that part of the extraction liquid, and the componentdissolved therein leaving the tubes at the above-mentioned first end ofthe column, is mixed into the particle material to be supplied to thecolumn.
 6. Method according to claim 1, characterized in that themixture of extraction liquid and extracted particle material leaving thecolumn at the above-mentioned second end is separated and the additionalextraction liquid resulting therefrom pumped back to the above-mentionedsecond end.
 7. Method according to claim 1, characterized in that themethod is carried out continuously.
 8. Device for removing a componentfrom solid particle material by extraction according to claim 1,comprising a column (1) in which at least one tube (2) extends, saidcolumn having a first and second end, means (18) for feeding extractionliquid into the column at the second end thereof, and scraping means atthe first end of the column for scraping off particle material from apacked porous bed, characterized in that in the wall of each tube (2) atleast one filter (3) is fitted, that at the first end the outlet (8) isconnected to the tube (2) or tubes, and a washing chamber (12) issituated near the scraping means (11) so that scraped off particles aredischarged via said washing chamber (12).